Presence of a virulence-associated plasmid in Yersinia pseudotuberculosis.

We have shown that Yersinia pseudotuberculosis can possess plasmids which are similar in size and function to the previously described Vwa plasmids of Y. enterocolitica. These plasmids are associated with the production of V and W antigens (calcium dependency) and pathogenicity of the organism. Further investigation of these plasmids from Y. pseudotuberculosis and Y. enterocolitica with restriction endonucleases revealed significant differences in their fragmentation pattern.

Plasmid associated with pathogenicity and calcium dependency of Yersinia enterocolitica.

Studies of the virulence and plasmid properties of Yersinia enterocolitica revealed a plasmid, 42.2 +/- 1.1 megadaltons in size, which is associated with the pathogenicity and calcium dependency of this organism.

Characterization of transmissible genetic elements from sucrose-fermenting Salmonella strains.

Two of seven sucrose-fermenting Salmonella strains obtained from clinical sources were found capable of conjugal transfer of the sucrose fermentation (Scr+) property to the Escherichia coli K-12 strain WR3026. The genetic elements conferring this Scr+ property, designated scr-53 and scr-94, were then conjugally transmissible from Escherichia coli WR3026 Scr+ exconjugants to other strains of Escherichia coli at frequences of 5 times 10- minus 6 to 5 times 10- minus 3 for the scr-53 element and 10- minus 6 to 10- minus 5 for the scr-94 element. In Escherichia coli hosts, both of these elements were compatible with F-lac and with each of six previously characterized transmissible lac elements. No antibiotic resistance characteristics or colicin production were discovered to be associated with either scr-53 or scr-94. Neither scr element generated a male host response to the female-specific phage phiII, but the scr-53 element rendered its Escherichia coli host sensitive to the male-specific phage R-17. Escherichia coli hosts containing scr-53 were susceptible to lysis by P1vir, and transduction of the scr-53 element was accomplished with this phage. The scr-53 element was isolated from Escherichia coli WR3026, Scr+ transductants, and Escherichia coli WR2036 Scr+ exconjugants as a covalently closed circular deoxyribonucleic acid molecule with a molecular weight (determined by electron microscopy) of approximately 52 times 10-6. Receipt of the scr-94 element rendered Escherichia coli hosts of this element unsusceptible to lysis by P1vir, although adsorption of the phage by an Escherichia coli WR3026 exconjugant containing scr-94 occurred as efficiently as it did on WR3026 itself. Repeated examination of Escherichia coli strains harboring scr-94, as well as of the Salmonella strain which initially contained it, did not reveal the presence of circular deoxyribonucleic acid. The synthesis of the sucrose cleaving enzyme was inducible in Escherichia coli exconjugants containing either scr-53 or scr-94.

Isolation and characterization of circular deoxyribonucleic acid obtained from lactose-fermenting Salmonella strains.

Six lac elements originally contained in Salmonella strains were transferred to Escherichia coli WR3026. All of the six E. coli strains that received one of the lac elements were observed to contain supercoiled, circular deoxyribonucleic acid (DNA) when examined by the dye-buoyant density method. Segregants of each of these E. coli WR3026 strains that had lost the ability to utilize lactose, when examined in the same manner as the lactose-fermenting strains, were not observed to contain these supercoiled, circular DNA molecules. Thus the DNA of the lac elements is maintained in E. coli WR3026 in the supercoiled, circular form. Molecular weights of the supercoiled, circular molecules isolated from strains carrying the lac elements were determined by sucrose density gradient centrifugation to be 30 million to 56 million. The calculated number of copies per chromosome of the lac elements varied from 1.4 to 3.7, depending upon the particular lac element examined. Each of the elements was determined to have a guanine plus cytosine composition of 50%. All six of the E. coli WR3026 strains containing a transmissible lac element were tested with the E. coli male-specific phage, R-17, and the E. coli female-specific phage, phiII, and did not respond to either of these phages as do F-containing derivatives of E. coli K-12.

Conservation of Salmonella typhimurium deoxyribonucleic acid in partially diploid hybrids of Escherichia coli.

Partially diploid Escherichia coli K-12 hybrids recovered from mating with a Salmonella typhimurium Hfr strain were found to differ with respect to the manner in which they conserved the added Salmonella deoxyribonucleic acid (DNA). Five of the diploid hybrids examined appeared to maintain the Salmonella DNA as part of a functional F-merogenote; these hybrids were sensitive to the male-specific phage, R-17, responded as males to the female-specific phage, phiII, and transferred their inherited Salmonella genetic markers at high frequency in conjugation experiments. Six diploid hybrids were observed which were not sensitive to R-17, and from which the added Salmonella DNA was not transmissible in conjugation tests; nevertheless, these hybrids responded as males to phiII, and the Salmonella chromosomal fragments were conserved in them as parts of supercoiled, circular DNA elements. It was concluded that these circular DNA elements were defective F-merogenotes, unable to direct the synthesis of F-pili. Three diploid hybrids were found which were not sensitive to R-17, and which responded as females to phiII; no circular DNA was found in them, and it was concluded that their conservation of the Salmonella genetic fragments was accomplished in some manner which did not involve association with F or assumption of the supercoiled circular configuration. Other partially diploid hybrids were observed which appeared similar to these latter three hybrids with regard to their conservation of the Salmonella DNA, but which also contained an infecting F-factor; in these hybrids, both genetic and molecular experiments indicated that the unstably conserved Salmonella DNA was not associated physically with the F-factor.